I have GDM XDMCP enabled. However, when I select on the GDM screen to login to a remote system via XDMCP, the system scans the netowrk and then returns a claim of No Serving Hosts Were Found.

I know this is wrong, because another box on my network is also XDMCP enabled, and its GDM chooser is only showing itself as an available host.

Both systems are running Debian Unstable. The one that can at least see itself is running an older version of GDM (I have no idea what version). The other one that sees nothing on the network is running whatever the latest GDM in the Debian repositories is.

Any ideas how to fix this so others can log in remotely to this box?